Hot melt adhesives are employed in the most varied industries in order for parts to be interconnected. Simple manual apparatuses or automated application systems are available for preparing and supplying adhesive to the most varied substrates.
Automated application systems are very often employed in the manufacturing processes of products. The application systems are in most instances adapted to the respective manufacturing process of products and are composed of apparatuses and machine parts which are suitable for the process. Standard apparatuses are used in order for the variants of embodiments of apparatuses to be minimized, said standard apparatuses in combination with specific adhesive applicator heads or adhesive application equipment then forming a system that is optimized for the process.
For example, an adhesive application apparatus which includes the following functions is used: The adhesive to be melted is placed in a pre-melting tank, or is supplied by way of an automatic supply system, such as a granules conveyor, for example. The still solid adhesive is heated and, on account thereof, liquefied in the pre-melting tank. The liquid adhesive makes its way into an adjoining reservoir region that belongs to the pre-melting tank. A conveying pump conveys the liquid adhesive from the reservoir region by way of a hose to one or a plurality of adhesive applicator heads. Switchable valves by way of which the application of adhesive can be switched on or off on account of control signals are attached in the applicator heads. An adhesive melting apparatus is employed if a roller application system is to be employed instead of the applicator heads. By contrast to the adhesive application apparatus, the liquid adhesive is not supplied to the adhesive applicator heads but is conveyed into a reservoir tank in which rollers rotate. A fill level sensor which checks the fill level of adhesive is attached in the reservoir tank. If adhesive is required, the fill level sensor signals this requirement to the controller of the adhesive melting apparatus, and the apparatus conveys liquid adhesive into the reservoir tank until the fill lever sensor signals that there is no longer any requirement.
The adhesive in the adhesive application apparatus and in the adhesive melting apparatus is converted from the solid state to the liquid state by the influence of heat. Depending on the adhesive, the latter in the non-heated solid state has various forms of delivery. The forms of delivery can be granules, pellets, or small blocks. Candles having a weight of 2, 3, or 20 kilograms are also employed.
A device for providing a free-flowing medium in a controlled manner is described in EP 1 447 143 A2. Said device comprises a container for receiving adhesive, and a melting device for causing an increase in temperature. The melting device has an exit region having at least one passage for the free-flowing adhesive. If and when the melting device is heated the adhesive that is in direct contact with the melting device melts and makes its way through the at least one passage into the following storage unit. It has been demonstrated in practice that the melting device has to be provided with a plurality of passages in order for the liquid adhesive to be able to positively flow out, and that the passages have to have a diameter which is larger than the grain diameter of the granules. On account thereof, the device is unsuitable for melting adhesive in the form of granules. The granule bodies in a non-melted state can make their way through the passages into a storage unit, and the contact area between the melting device and the granules is small. This leads to a low melting rate. A press having a follow-up plate is provided for adhesive blocks or adhesive candles, in order for the melting rate to be increased. The use of the press having the follow-up plate requires an additional effort and renders the entire device expensive.
A hot melt glue melting device having a melting grill with a multiplicity of passage openings for melting hot melt glue is proposed in EP 2 650 095 A1. The passage openings have an opening width that corresponds to 0.3 to 0.8 times the dimension of the smallest granule particles. The device is conceived for melting hot melt glue which is delivered in the form of granules. The arrangement of a first heating installation in the external region of the melting grill restricts the choice of the overall dimensions of the melting grill. The heat has to be introduced into the melting grill by thermal conduction. The use of a second heating installation in the center of the melting grill demonstrates that the heat output is limited and only a relatively small melting grill area is available for melting the adhesive. This may suffice for the envisaged application of gluing filter paper in products of the tobacco-processing industry. The area of the proposed melting grill is insufficient for adhesive melting apparatuses or adhesive application apparatuses which have to melt adhesive in small as well as large amounts.
Furthermore, melting of adhesive in the form of blocks or candles is implementable only under certain conditions. The available surface that can contact the adhesive is too small.
A device of the type mentioned at the outset is known from EP 1 115 542 B1. The hot melt glue melting device described therein has a melting grill which has a plurality of downwardly extending elongate grill elements in the form of ribs which are thermally connected to a heating element. A reservoir container has a plurality of upwardly extending thermal transfer elements that are configured as ribs and are connected to a heating element. The elongate grill elements herein engage in the upwardly extending thermal transfer elements. Furthermore, the downwardly extending grill elements have further ribs. A first and a second set of ribs point upward and are mutually orthogonal. Said first and second set of ribs herein form a grill structure having openings through which the liquid adhesive can flow into the reservoir container. The first and the second set of ribs herein have dissimilar heights such that solid adhesive in the form of pellets, blocks, or candles, does not simultaneously touch both rib ends when said adhesive comes to lie on the ribs. On account thereof, the higher heated ribs intrude into the solid adhesive at a faster rate, on account thereof enabling a high melting rate also in the case of these forms of delivery of adhesive. The elongate grill elements by way of a third set of ribs engage in the thermal transfer elements. Such a melting grill is very complex in manufacturing. High apparatus costs arise on account thereof. This represents a major disadvantage of the device. On the other hand, the shape of the melting grill is not modifiable if and when the latter is installed in a hot melt glue melting device. The melting grill is modified for melting adhesive in the form of granules or pellets, and in the form of blocks or candles, when a high melting rate is to be achieved. A high melting rate thus cannot be achieved for all forms of delivery of the adhesive by way of the hot melt glue melting device.